For convenience, in this patent specification, the term “shoe” will be used for an article of footwear that includes a cushioned sole. Examples include athletic shoes such as running shoes, soccer/football shoes, basketball shoes, baseball shoes, cross-training shoes, cycling shoes or tennis shoes. The term can also refer to hiking boots, dress shoes, loafers, sandals, work boots and specialized footwear that includes a cushioned sole. Moreover, in the context of this specification, the term “shoe” embraces articles of footwear having a sole assembly comprising an outsole which contacts the ground, an insole which usually will be the uppermost permanent part of the sole and a cushioning section intermediate the insole and the outsole. Usually the insole will be attached by its periphery to the shoe upper and may be covered by a replaceable insert of foam rubber or the like.
The term “cushioning” refers to an insert within the sole assembly that cushions impact, such as an air bladder or a foam insert.
Examples of shoes that have intermediate cushioning of one form or another between the outsole and the insole are disclosed in US patent documents numbers U.S. Pat. Nos. 7,870,681; 8,312,646; 2011/0041359; 2012/0023778; 2011/0025159; 2013/0025075 and the present inventor's own Canadian patent number 2,538,931.
In use, and in particular athletic use or other uses that subject shoes to high levels of forces, the cushioning portion of the shoe may be subjected to lateral, longitudinal (i.e. axial or fore/aft), compressive and tensile forces, either unidirectionally or in various combinations simultaneously or in rapid succession. For example, multiple forces on the sole may occur as the wearer stops, starts, changes direction, jumps, and so on. Also, sports shoes used in, for example, basketball or other sports involving rapid changes in direction and stopping abruptly may stretch the material of the shoe upper and lead to problems with stability and load distribution of the shoe. In US2013/0025075, US2012/0023778 and others, these problems have been addressed by, in effect, a mesh or lattice-work of intersecting strands either embedded into or attached securely to the outside of the sidewalls of the shoe upper. The strands interconnect an area of the shoe upper adjacent the lace eyelets and an area of the shoe upper at or adjacent the outsole and/or to the outsole itself. The intersecting sets of strands are said to limit stretching of the side walls of the shoe upper.
Stability and load distribution problems may be particularly significant in shoes which have a relatively thick and/or compliant cushioning section between the outsole and the insole. Such problems can arise with cushioning of the kind comprising an air bag or bladder or a plurality of air pockets or cells distributed about the sole of the shoe between the outsole and the insole. Both kinds of air cushioning members may be susceptible to lateral or axial instability which can lead to lateral “roll over” of the shoe, lateral instability or other problems during use. Instability can also arise when the cushion is subjected to unbalanced vertical compressive forces. Similar considerations apply to shoes which have an outsole having several segments each connected by sidewalls to a midsole of the sole section, with air or foam rubber in the cavity defined thereby. Such a shoe is marketed as a Bounce™ or Leaf Spring Bounce™ by Adidas Group.
Where a plurality of air cells are used, some stability may provided by the walls of the cells, which may comprise rubber, resilient synthetic plastics materials or the like which are designed to be somewhat rigid to reduce lateral instability. A similar solution can be provided with a monolithic bladder as the cushion.
In general, the sidewalls of air cells or air bladders should be somewhat flexible in order to allow the cell(s) or bladder to compress, so as to take advantage of the compressive properties of the air bladder. However, in the absence of means to improve stability, a flexible sidewall tends to have less lateral stability which can increase the tendency of the shoe to roll over or for the sole to be displaced laterally or axially relative to the upper when subjected to horizontal stresses (lateral or axial) or imbalanced forces. As a result of these competing requirements, shoe design often involves a trade-off or compromise between the requirements for stability and cushioning.
In some cases, a solution has been sought by incorporating strands in the sidewall of an airbladder to increase lateral stability. Although the use of strands for reinforcing the sidewalls of the shoe upper may make the shoe upper less stretchable, and air cell walls and/or hydraulic stabilizers may improve stability, the above-mentioned ways of providing cushioning and stability between an outsole and insole separated by an intermediate cushioning section, especially comprising an airbag/bladder, are not entirely satisfactory in that these structures can reduce the vertical compressibility of the sole, thereby reducing shock absorption.
An alternative means to improve stability may be provided by one or more hydraulic members as disclosed, for example, in the present inventor's Canadian patent number 2,538,931.